The present invention relates to an ink-jet printer, and more particularly, to an ink-jet printer with an ink nozzle purging device for purging an ink nozzle of a printing head of the ink-jet printer.
Well known is an ink-jet printer which controls ink ejection onto a recording medium such as a recording paper from a plurality of ink nozzles formed in a printing head in an orderly manner to record a desired image on the recording medium. The ink-jet printer has widely been used in recent years, since the ink-jet printer is more excellent in running cost and printing speed as compared to an ink ribbon printer which transfers a desired image from a thermal transfer ink ribbon with a thermal head on a recording medium so that the image is recorded on the recording medium.
In the ink-jet printer, however, printing is hindered by ink clogging in the ink nozzle and a bubble generated in an ink passage extending from an ink tank or an ink cartridge to the ink nozzle. Hence, it is important to prevent the ink clogging and bubble generation in the ink passage in order to obtain a good printing result every time when the ink-jet printer is used.
In recent years, more precision of an image to be recorded on a recording medium has been made demanded and a nozzle diameter has progressively been smaller in accordance with this trend. As the nozzle diameter has been made smaller, though, the problem of the ink clogging at an ink nozzle has become more serious.
Moreover, in recent years, a further improvement of a printing speed has strongly been desired. In order to meet this desire, the following technical progress has been achieved in a method for recording an image on a recording medium by using a printing head. That is, while a small printing head had conventionally been reciprocated along a direction crossing a feed direction of a recording medium, in recent years a reciprocation of a printing head in the crossing direction has been unnecessary by designing a length of the printing head along the crossing direction so as to be almost the same as a length of the recording medium along the crossing direction (or a width of the medium).
As the length of the printing head is larger, the number of ink nozzles formed in the printing head increases and a length of an ink passage increases as well. Consequently, a more effective preventing device against the ink clogging and bubble generation has been demanded.
Such preventing devices have been known publicly by the published Jpn. Pat. Appln. KOKAI Publication No. 3-184872 published on Aug. 12, 1991 and the published Jpn. UM Appln. KOKAI Publication No. 59-48838 published on Mar. 31, 1984.
In an ink-jet printer disclosed in the published Jpn. Pat. Appln. KOKAI Publication No. 3-184872, ink is fed to a printing head 2 having a plurality of ink nozzles 2a through an ink supply pipe 3 equipped with a plurality of opening/closing valves 4, 5 from an main ink tank 1, and an ink circulation pipe 6 extends from the printing head 2 to the ink supply pipe 3 through an electromagnetic valve 7, an auxiliary ink tank 9 and a circulating pump 10. In a case where an ordinary image recording is performed, the printing head 2 is operated while the opening/closing valves 4, 5 are both closed, the electromagnetic valve 7 is opened and the circulating pump 10 is operated. If an ink level in the auxiliary tank 9 is lowered beyond a predetermined level, the opening/closing valves 4, 5 are both opened, the electromagnetic valve 7 is opened and the circulating pump 10 is activated. As a result of the procedures, the ink is fed from the main tank 1 into the auxiliary pump 9. Before the ordinary image recording begins, the opening/closing valve 5 located in the main ink tank 1 side on the ink supply pipe 3 is closed, the opening/closing valve 4 located in the printing head 2 side on the ink supply pipe 3 is opened, the electromagnetic valve 7 is opened and the circulating pump 10 is activated, while all of the plurality of ink nozzles 2a are made open in the printing head 2. As a result of the procedures, the ink circulates through the ink supply pipe 3, the printing head 2, and the ink circulation pipe 6. If a bubble is included in the ink, the bubble is discharged to the outside through the ink nozzles 2a. And a small amount of ink is also ejected through the ink nozzles 2a to clear ink clogging in the nozzles.
In an ink-jet printer disclosed in the published Jpn. UM Appln. KOKAI Publication No. 59-48838, an ink filter 3, electromagnetic valves 12, 13 and an ink pressurizing means 5 are equipped in ink pipes 9, 10 extending from an ink cartridge 1 to a recording head 4. The ink pressurizing means 5 is driven by an electromagnetic coil 82 (in an embodiment of FIG. 1), a combination of a motor 20 and a cam 21 (in an embodiment of FIG. 2) or a combination of a motor 30 and gears 31, 32 (in an embodiment of FIG. 3). In the case of an ordinary recording, the electromagnetic valves 12, 13 are opened, an operation of the ink pressurizing means 5 is stopped, and the ink is supplied from the ink cartridge 1 to the recording head 4 through the ink pipes 9, 10. When an ink nozzle, not shown, of the recording head 4 is purged, a piston 7 of the ink pressurizing means 5 is pressed while the electromagnetic valve 12 located in the ink cartridge 1 side on the ink pipe 9 is closed, and a pressure of the ink in the recording head 4 and in the ink pipe 10 located in the recording head 4 side is increased. After the ink nozzle is purged, the piston 7 of the ink pressurizing means 5 is returned back while the electromagnetic valve 13 is closed, and the ink pressurizing means 5 is filled with the ink flown out from the ink cartridge 1 through the ink pipe 9 located in the ink cartridge 1 side.
A structure for ink nozzle purging in the ink jet printer disclosed in the published Jpn. Pat. Appln. KOKAI Publication No. 3-184872 has a disadvantage that a large quantity of the ink is leaked out from the plurality of nozzles 2a of the printing head 2 because the ink is pressurized only by an action of the circulating pump 10 when the plurality of ink nozzles 2a of the printing head 2 are to be purged. This disadvantage is caused by that a long time is required for pressurizing the ink by the circulating pump 10 to a desired value necessary for the ink nozzle purging and for reducing the pressure of the ink to a pressure lower than the desired value after the ink nozzle purging is finished. The disadvantage becomes greater as the number of the ink nozzles 2a is increased.
In a structure for ink nozzle purging in the ink jet printer disclosed in the published Jpn. UM Appln.
KOKAI Publication No. 59-48838, as the number of printing heads 4 which are used in the ink jet printer is increased, the number of necessary ink pressurizing means 5 is also increased. Since the ink pressurizing means 5 is driven by the electromagnetic coil 82 (in the embodiment of FIG. 1), the combination of the motor 20 and the cam 21 (in the embodiment of FIG. 2) or the combination of the motor 30 and the gears 31, 32 (in the embodiment of FIG. 3), the number of wirings required for the electromagnetic coil 82 or the motors 20, 30 are increased, so that the structure of the ink nozzle purging device becomes complex and expensive.
The present invention has been derived from under such circumstances and an object of the present invention is to provide an ink-jet printer with a low cost ink nozzle purging device in which even if the number of printing heads which are used in the ink-jet printer or a size of each of the printing heads is increased or the number of ink nozzles formed in each printing head is increased, not only the ink nozzles can be surely purged but also a bubble in each printing head or in an ink supply pipe between an ink tank or an ink cartridge and the printing heads can be surely removed, besides, an amount of a leakage of the ink necessary for ink nozzle purging and discharging the bubble can be limited as small as possible and furthermore, a structure of the ink nozzle purging device does not become complex.